Conventionally, a method of obtaining a silicon single crystal for use in, for example, semiconductor devices and solar batteries as a single crystal ingot by using the CZ method has been widely used. FIG. 5 shows a schematic view of a silicon single crystal manufacturing apparatus that is generally used. As shown in FIG. 5, in the silicon single crystal manufacturing apparatus 20, vertically movable crucibles 22 and 23 that accommodate a silicon melt 21, and a heater 24 that is arranged so as to surround the crucibles 22 and 23 are generally arranged in a main chamber 26 where a single crystal 25 is grown. A pulling chamber 27 for accommodating and taking out the grown single crystal 25 is continuously provided above the main chamber 26.
For the purpose of discharging oxides generated in a furnace out of the furnace etc., an inert gas such as argon gas is introduced into the chambers from a gas inlet 28 provided at an upper portion of the pulling chamber 27. The inert gas is guided so as to flow near the single crystal 25 by using a graphite gas flow-guide cylinder 30, and discharged from a gas outlet 29. A seed crystal 31 is brought into contact with the silicon melt 21 and the single crystal 25 is then grown.
There has been known two pulling methods. One of the methods is an atmospheric pressure method in which the single crystal is pulled in an atmosphere inside the furnace that is maintained at approximately an atmospheric pressure. The other method is a reduced pressure method in which the single crystal is pulled in a reduced pressure atmosphere inside the furnace that is brought to a low vacuum area (10 to 500 hPa). The reduced pressure method is now more common.
In the above manufacture of the silicon single crystal, the inert gas discharged from the silicon single crystal manufacturing apparatus 20 includes silicon oxide generated in the apparatus and an impurity gas, such as CO, CO2, O2, N2, H2, and the like.
In recent years, the required amount of the inert gas has increased as silicon single crystal manufacture has increased in scale. Collecting and recycling the inert gas discharged from the silicon single crystal manufacturing apparatus have been accordingly important for reduction of cost. To realize this, it is necessary to remove the above-described silicon oxide and impurity gas contained in the discharged inert gas and purify it.
Conventionally, a facility in which an oil-sealed rotary vacuum pump, a gas purification unit, and the like are connected to the silicon single crystal manufacturing apparatus are common for recycling the inert gas. In the facility, however, there is a problem in that an oil mist, which is difficult to be separately collected, is mixed to the inert gas that is heated at a high temperature and that is then discharged from the silicon single crystal manufacturing apparatus, since the vacuum pump uses an oil. This oil mist causes environmental pollution when it is emitted to air. A water ring vacuum pump has been also used to avoid this problem. However, the water ring vacuum pump needs a large amount of water and consumes a large amount of electric power, and its cost thus becomes high.
Accordingly, a dry type pump, so-called a dry pump, has been becoming more common since it can reduce cost more than the two wet type pump described above. For example, there is described an inert gas recycling apparatus provided with, behind the dry pump, a wet type bubbler, an electric fine particle collector, and a purification unit etc. (See Patent document 1).
A method for removing fine particles, such as fine powders of silicon oxide, contained in a gas discharged from a single crystal manufacturing furnace by introducing the gas into a venturi scrubber has been known (See Patent document 2).
When the above-described conventional apparatus and method are used to remove the silicon oxide contained in the inert gas, however, the silicon oxide cannot be removed sufficiently since the silicon oxide is a fine powder of the order of several microns in size, its maintainability becomes low, and its operation cost becomes high.